In-mold labeling method

ABSTRACT

Extrudable labelstock for in-mold labeling purposes which has a tensile ultimate elongation per ASTM D-882 of at least about 10% in one or both of the machine and transverse directions, and which contains a sufficient amount of one or more slip additives to prevent a significant degree of edge-welding between adjacent stacked sheets of the labelstock on a high type die cutter in an in-mold labeling process, and the improved in-mold labeling process employing such labelstock.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of application Ser. No. 07/485,333 filed Feb. 29,1990 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to film labelstock, and particularly toextrudable film labelstock for in-mold labeling purposes, wherein gooddie-cuttability, printability, and/or contact clarity are desirable.

2. Brief Description of the Prior Art

The conversion of labelstock into labels for in-mold labeling involvesthe printing, sheeting, stacking, and die-cutting of the labelstock on ahigh type die cutter. A number of commercially desirable filmstocksexhibit an economically significant degree of edge welding betweenadjacent stacked sheets of film in die-cutting on such apparatus,however, such that individual labels cannot be properly formed anddispensed in the in-mold labeling process.

Consequently, polyethylene and a number of related highly extensible,inexpensive film materials have not heretofore proven to be economicallyuseful alternatives for in-mold labeling, unless modified in somefashion so that the filmstock to be die-cut possesses a tensile ultimateelongation in both the machine and tensile directions, as determined byASTM D-882, on the order of about 50% or less. It is noted that in factsome labelstocks, notably some polystyrene labelstocks, have die cutacceptably at the label thicknesses typically employed (i.e., 3-4 mils)in the in-mold labeling industry even with tensile ultimate elongationsof from 45-50%, but for labelstocks generally it is considered that thelower figures represent an acceptable degree of extensibility at thesetypical thicknesses and in the commercial in-mold labeling processes.

Usually the films displaying a tensile ultimate elongation of thismagnitude, i.e., the films which have to date proven sufficientlyresistant to edge-welding to be of practical use in an in-mold labelingprocess of the type described, are either very highly biaxiallyoriented, or are highly filled with inorganic fillers, or possess avoided structure. Achieving a high degree of biaxial orientationrequires comparatively expensive machinery relative to conventionalblown and cast film apparatus. Highly filled filmstocks and those with avoided structure generally have a roughened surface which is notamenable to printing and exhibit poor contact clarity.

Recently-issued U.S. Pat. No. 4,883,697 (the '697 patent) to Dornbuschet. al. discloses a label for in-mold labeling wherein a thermoplasticlabel stratum is joined by coextrusion or preferably by an interveningadhesive layer to a stress-compensating stratum. The stress-compensatingstratum is coated with a low temperature sealant layer such a theethylene-vinyl acetate copolymer-paraffin-microcrystalline wax mixturedescribed in U.S. Pat. No. 3,753,125 to Elliott. The thermoplastic labelstratum can be polypropylene or other materials having a Young's modulusof greater than 100,000 psi, while the stress-accommodating stratum canbe formed from materials such as low density polyethylene orethylene-vinyl acetate copolymers having a Young's modulus of less than40,000 psi.

Recently-issued and commonly-assigned U.S. Pat. No. 4,387,075 to Dudleydiscloses a coextruded label for use in in-mold labeling also, butrelies on a surface printable layer of polystyrene.

While it is considered that films of the type described in the U.S. Pat.No. 4,883,697 would possible die cut acceptably and without asignificant degree of edge welding, the patent does not teach or suggestan acceptable, wholly extrudable film labelstock which utilizes theedge-welding but inexpensive materials such as high densitypolyethylene, and which further presents a smooth surface for printingand excellent contact clarity.

Such a labelstock would be desirable from the perspective of enablingthe economical use in an in-mold labeling process of materials which,despite their attractiveness as relatively inexpensive and effectivelabel materials, previously have not been generally so used because ofedge-welding between stacked sheets of the materials in die-cutting on ahigh type die cutter. The labelstock would further prove advantageous inbeing wholly extrudable rather than requiring an additional coatingstep, and by conventional blown and cast film processes and equipment.The absence of fillers in the labelstock such as would create a roughsurface for printing or cause poor contact clarity in the labels wouldbe a further desirable aspect.

SUMMARY OF THE INVENTION

The present invention provides a film labelstock which meets these needsand which overcomes the shortcomings of the prior art relating tolabelstock particularly for in-mold labeling.

In one aspect, the present invention relates to an extrudable filmlabelstock characterized by a tensile ultimate elongation in one or bothof the machine and transverse directions of at least about 10% accordingto ASTM D-882, and having a sufficient amount of one or more slipadditives incorporated therein such that stacked sheets of thelabelstock will die cut on a high type die cutter without a significantdegree of edge-welding between the sheets.

In another aspect, the invention relates to a label manufactured fromthe labelstocks of the present invention and to an article to which thelabel is applied, and more particularly relates to labels wherein aninner surface of a surface printable layer carries printed matter ratherthan an exposed outer surface of the label. "Inner" and "outer" in thisrespect are thus understood as being determined relative to an articleto which the label is applied, and to the opportunity for theenvironment in which the label is used to act upon the printed matter.

In still another aspect, the invention provides processes or inhibitingedge welding in the die cutting generally of extrudable film materialscharacterized by a tensile ultimate elongation in one or both of themachine and transverse directions of at least about 10% according toASTM D-882, and particularly in the die-cutting of film labelstocks socharacterized for in-mold labeling. Also provided is an improved in-moldlabeling process of the type comprising the steps of forming a filmlabelstock by extrusion, printing on a surface printable layer of thefilm labelstock, forming the printed film labelstock into sheets,stacking the sheets, die cutting the stacked sheets to form labelstherefrom, and dispensing the die cut labels to one or more molds forapplication to an article to be labeled, wherein the improvementcomprises the step of incorporating a sufficient amount of one or moreslip additives in the film labelstock such that the stacked sheets ofthe labelstock will die cut on a high type die cutter without asignificant degree of edge-welding between the sheets.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic flow diagram of the process of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The extrudable film labelstock of the present invention is capable ofbeing manufactured in a wide variety of embodiments and with a varietyof materials, as will be readily appreciated. For purposes of thepresent disclosure, however, several embodiments are favored.

In a comparatively simple embodiment, the film labelstock will consistessentially of a surface printable layer, with the surface printablelayer having the one or more slip additives incorporated therein in anamount sufficient to permit the labelstock to be die cut on a high yedie cutter without a significant degree of edge-welding between stackedsheets of the labelstock.

Some degree of edge-welding is thus considered permissible. What isessentially expressed in the term "without a significant degree ofedge-welding" is the idea that the labelstock of the present inventionshould not possess the extent of edge-welding which has heretofore madethe use of film materials having a tensile ultimate elongation (per ASTMD-882) of at least a certain percentage and greater economically andpractically infeasible.

Preferably, however, the film labelstock of the present invention shouldrealize at least a twenty-fold reduction in edge-welding over thatexperienced with a labelstock identically constructed and processed butfor the omission of the one or more slip additives therefrom. Mostpreferably, the film labelstock with slip additives incorporated thereinaccording to the instant invention should realize at least athousand-fold improvement in edge-welding over a labelstock omittingthese slip additives.

The degree of edge-welding for purposes of this comparison is defined bythe percentage of edge-welded sheets of a given 3.5 to 5.0 mil thick,unprinted labelstock when cut on a high type die cutter.

In addition to the aforementioned slip additives, the surface printablelayer will preferably also be comprised of a thermoplastic materialsfraction selected from the group consisting of homopolymers of theolefins, copolymers of two or more of the olefins, and mixtures of suchhomopolymers and/or copolymers. Thus, for example, the surface printablelayer may comprise in addition to the one or more slip additives amixture of low density polyethylene and polypropylene, or a mixture ofan ethylene copolymer with polypropylene homopolymer, or a mixture ofone ethylene copolymer with a different ethylene copolymer, so long asthe surface printable layer retains a tensile ultimate elongation of atleast about 10% in one or both of the machine and transverse direction,as determined by ASTM D-882.

For a thermoplastic materials fraction constituted as described in thepreceding paragraph, it is considered that slip additives selected fromthe group consisting of stearamide, erucylamide, oleyl palmitamide, andstearyl stearamide, especially from about 0.15 to about 1.0 percent byweight of such slip additives (based on the weight of the surfaceprintable layer), will be useful for achieving an edge-weld inhibitingconcentration of slip additives at the interface between adjacent sheetsof stacked 3.5-5.0 mil thick, unprinted labelstock and thus acceptablelevels of die-cuttability on a high type die cutter, without at the sametime rendering the surface of the labelstock unsuitable for printing.

The thermoplastic materials fraction of the surface printable layer andthus of the film labelstock is more preferably comprised of low densitypolyethylene, medium density polyethylene, high density polyethylene, ormixtures thereof. Where the thermoplastic materials fraction is at leastabout 25 percent by weight, and most preferably about 100 percent byweight of high density polyethylene, it is expected that the twenty-foldimprovement in edge-welding alluded to earlier will be possible with theincorporation of at least about 0.25 percent by weight of slip additivesduring extrusion of the surface printable layer. It is further expectedthat the most preferred thousand-fold improvement will be possible withthe addition of at least about 0.50 percent by weight of the slipadditives, which slip additives again are selected from the groupconsisting of stearamide, erucylamide, oleyl palmitamide, and stearylstearamide.

The surface printable layer in this most preferred embodiment can alsocontain from about 0 to about 20 percent by weight of a pigment such astitanium dioxide.

In sum, the simple embodiment wherein the film labelstock consistsessentially of a surface printable layer would, in a most preferredembodiment, contain: at least about 0.5 percent but not more than 1.0percent by total weight of slip additives selected from the groupconsisting of stearamide, erucylamide, oleyl palmitamide, and stearylstearamide; a thermoplastic materials fraction of at least about 25percent and preferably about 100 percent by weight of high densitypolyethylene; and from about 0 to about 20 percent by total weight oftitanium dioxide.

In another embodiment of the film labelstock of the present invention,the film labelstock would again be characterized by a tensile ultimateelongation in one or both of the machine or transverse directions of atleast about 10%, but would comprise a surface printable layer of a firstfilm material and a supporting layer of a second material. The surfaceprintable layer and the supporting layer in this embodiment define firstand second outer surfaces, respectively, of the film labelstock, suchthat when the film labelstock of this embodiment is sheeted and stackedthe surface printable layer of a first sheet will be placed in intimatecontact with the supporting layer of a second sheet of labelstock.

The surface printable layer and the supporting layer collectivelycontain a sufficient amount of one or more slip additives in the firstand second materials comprising such layers so that edge-welding to asignificant degree is effectively prevented between adjacent stackedsheets of labelstock. Generally the one or more slip additives will bepresent in a combined amount of from about 0.15 to about 1.0 percent byweight of the combined weights of the surface printable layer and thesupporting layer.

Preferably the surface printable layer is otherwise constituted in thisembodiment substantially as described in the simpler embodiment detailedabove, with the first material thus comprising a thermoplastic materialsfraction which is most preferably from at least about 25 percent toabout 100 percent by weight of high density polyethylene, and containingfrom about 0 to about 20 percent by weight of the layer of a pigmentsuch as titanium dioxide.

The supporting layer in a preferred embodiment is a heat activatableadhesive substrate layer substantially of the type described in detailin commonly-assigned U.S. Pat. No. 4,837,075 to Dudley, which patent ishereby incorporated herein by reference. Briefly, however, the secondfilm material in this preferred embodiment of the supporting layercomprises a polymeric fraction selected from the group consisting of:(a) homopolymers of ethylene; (b) copolymers of ethylene with one ormore alpha olefins having from 4 to 8 carbons; (c) mixtures of (a) and(b); and (d) mixtures of either (a), (b), or (c) with up to about 95percent by weight of one or more copolymers of ethylene and from about 1percent to about 30 percent by weight of a copolymerizableethyleneically unsaturated carboxylic acid or ester containingcomonomer. Most preferably, the heat activatable adhesive substratelayer will be comprised of a mixture falling into the (d) group ofmixtures, wherein the mixture will contain more than about 35 percent byweight of one or more ethylene-vinyl acetate copolymers.

The most preferred embodiment of the at least two layer construction ofthe film labelstock of the present invention, in other words of theembodiment having at least a surface printable layer defining a firstouter surface of the labelstock and a supporting, heat activatableadhesive substrate layer defining a second opposing outer surface of thelabelstock, would have a surface printable layer consisting essentiallyof at least about 25 percent, and preferably about 100 percent, byweight of high density polyethylene.

The remainder of the surface printable layer would comprise from 0 toabout 75 percent by weight of other materials selected from the groupconsisting of pigments, slip additives selected from stearamide,erucylamide, oleyl palmitamide, and stearyl stearamide, and otherethylene homopolymers and copolymers.

The heat activatable adhesive substrate layer would have a polymericfraction selected from the categories (a)-(d) of materials enumeratedabove, and would further contain one or more slip additives in the formof stearamide, erucylamide, oleyl palmitamide, and stearyl stearamide,with the total amount of such slip additives in the surface printablelayer and adhesive substrate layer being from about 0.50 to about 1.0percent by weight of the combined weights of the surface printable layerand adhesive substrate layer.

In general terms, the thicknesses of the respective layers and theamounts and types of slip additives contained in each will be tailoredto enhance or at least not cumulatively significantly adversely affectthe performance of the labelstock in aspects other than die-cuttabilityand the prevention of edge-welding, the slip additives again howeverbeing generally resent in the surface printable and adhesive substratelayers in an amount of from about 0.15 to about 1.0 percent by weight ofthe combined weight of these layers.

The embodiments which have been described reflect the discovery that theprovision of slip additives in the outer layers of an extrudable filmlabelstock can, with a proper loading and selection of such additives inouter layers of certain natures, impart a resistance to edge welding insheets formed from the extruded labelstock when the sheets are die cuton a high type die cutter in an in-mold labeling process. The use offilm materials and labelstocks which had previously proven tooextensible to be of economically practical value in such processes, suchas high density polyethylene film labelstocks, for example, is thusenabled. The specific embodiments detailed above are thought to reflectseveral useful applications of this discovery wherein contact clarity,surface smoothness, and the amenability of the labelstocks to printingare not significantly compromised.

It will accordingly be understood that numerous other labelstockconstructions are within the spirit of the present invention, and arewithin the design skills of a person of skill in the art to which thepresent invention most closely pertains. For surface printable layersand supporting or heat activatable adhesive substrate layers comprisedof different materials than those specified above but wherein thelabelstock may nevertheless still be characterized as too extensible todie-cut on a high type die cutter without added slip additives, it maybe found for example that certain slip additives may be more effectivein achieving a concentration adjacent a first or second outer surface.In this manner, lesser amounts of the slip additives are necessary toachieve the desired edge-weld inhibiting concentration of slip additivesat an interface between the surface printable layer of a first sheet oflabelstock and the support layer of an adjacent second stacked sheet.

Or, it may be that certain slip additives are desirably incorporated ina surface printable layer in greater concentrations than the same orother slip additives in the support layer, although typically fromconsiderations of printability the slip additives will be present in thesupport layer in significantly greater concentrations and may beincorporated substantially exclusively therein if the balance of otherproperties of interest suggests.

It is also to be understood that the extrudable film labelstocks of thepresent invention may desirably comprise other extrudable layers inaddition to a surface printable layer and a supporting or heatactivatable adhesive substrate layer, such as a regrind layer in themanner of U.S. Pat. No. 4,837,075. The film labelstocks of the presentinvention may thus essentially contain a surface printable layer eitheralone or in combination with a supporting layer carrying all or some ofthe slip additives, or may comprise the surface printable layer with asupporting layer and a number of intervening layers wherein slipadditives may or may not be distributed, dependent on whether the slipadditives are incorporated only in the materials comprising thesupporting and surface printable layers or in the materials of the otherlayers as well. Each of these variations is considered to be within thescope and spirit of the present invention, as defined by the claimswhich follow closely hereafter.

With reference of FIG. 1, there is shown a schematic flow diagram of oneembodiment of the process of the present invention comprising the stepsof forming a film labelstock comprising at least a surface printablelayer by extrusion, 11; incorporating edgewell inhibiting concentrationof one or more additives in the film labelstock such that the stackedsheets of the labelstock will die cut on the high type die cutterwithout significant degree of edge-welding between the sheets, 12;printing in the surface printable layer of the film labelstock, 13;forming the printed film labelstock into sheets, 14; stacking the sheets15; die-cutting the sheets on a high type die cutter 16; and dispensingdie-cut labels to one or more molds for application to an article to belabeled, wherein the film labelstock is characterized by an ultimatetensile elongation of at least about 10% in one or both of the machineand transverse directions when measured according to ASTM D-882.

The processes and apparatus by which the materials of the various layersin a film labelstock of the present invention are combined, and by whichthe labelstock is extruded, sheeted, stacked, and die cut areconventional and well know to the art. The processes and apparatus bywhich the labels are then dispensed for in-mold labeling to variousmolds and applied to articles formed in such molds are also well known,and need not be discussed in greater detail herein.

The invention is further illustrated by the following examples:

EXAMPLE 1

In this example a 5.0 mil thick two-layer labelstock was constructed bya cast film coextrusion of a surface printable layer and a heatactivatable adhesive substrate layer. The surface printable layercomprised a mixture of about 85.0% by weight of high densitypolyethylene (with a density in the range of 0.958 to 0.965 grams percubic centimeter and a melt flow rate of from 4 to 10 grams per 10minutes per ASTM 1238, condition E), 7.5% by weight of titanium dioxide,and 7.5% by weight of low density polyethylene (density of 0.922 gramsper cubic centimeter, and a melt flow rate of 1.15 grams per cubiccentimeter, and a melt flow rate of 1.15 grams per 10 minutes per ASTM1238, condition E). The heat activatable adhesive substrate layer wascomprised of: 84.0% by weight of an ethylene-vinyl acetate copolymerhaving a vinyl acetate content of 23 mol percent and a melt flow rate asdetermined by ASTM 1238 of 5.5 grams per 10 minutes; 10.0% by weight ofa second ethylene-vinyl acetate copolymer having a vinyl acetate contentof 28 mol percent and a melt flow rate of 6.0; 4.32% by weight of anethylene-vinyl acetate copolymer having a vinyl acetate content of about18 percent and a melt flow rate of about 2.5 grams per 10 minutes; 1.2%by weight of silicon dioxide; and equal amounts at 0.24% by weight eachof stearamide and erucylamide. The surface printable layer comprised 85%of the approximately 5.0 mil thickness of the labelstock as extruded,with the other 15% comprising the adhesive substrate layer.

The labelstock as thus constituted was sheeted, stacked and die cut on ahigh type die cutter. An inspection of a die cut stack of 50 sheets ofthe labelstock revealed that none of the sheets edge welded to theextent of being incapable of being individually dispensed on theapparatus typically used for this purpose, while an identicallyconstructed and processed labelstock omitting the slip additives showededge welding between 100% of the stacked sheets.

EXAMPLE 2

In this example an approximately 4.5 mil thick surface printable filmlayer was constructed by a blown film process. The surface printablefilm layer was comprised of a mixture of about 71.0% by weight of thelow density polyethylene described and used in Example 1, about 24.0% byweight of the high density polyethylene likewise described and used inExample 1, about 1.0% by weight of silicon dioxide, and about 3.6% byweight of the thylene-vinyl acetate copolymer used in Example 1 andhaving a vinyl acetate content of about 18 mol percent and a melt flowrate of 2.5 grams per 10 minutes. On stacking, sheeting and die cuttingin accordance with the treatment of the labelstock of Example 1, none ofthe 50 stacked sheets showed edge-welding of a significant extent ofadjacent sheets. A comparison surface printable film layer which wasidentically manufactured and processed, and which differed from thefirst layer only in the omission of the slip additives and itsreplacement by an equivalent amount by weight of the low densitypolyethylene, showed edge welding between 90% of the layers.

The above examples demonstrate that the labelstocks of the presentinvention are significantly less susceptible to edge welding thanequivalent labelstocks not containing the slip additives, and furtherthat coextruded labelstocks with surface printable, mostly high densitypolyethylene layers and heat activatable adhesive substrate layers arecapable of being made which do not exhibit a perceptible degree ofedge-welding at all.

It can be seen that the present invention is thus well adapted tofulfill the needs and desires set forth therefor above, and whilespecific embodiments have been described and exemplified herein, it willbe understood again that numerous changes of an obvious nature may bemade to these embodiments, without departing in spirit and scope fromthe invention defined by the following claims.

What is claimed is:
 1. An in-mold labeling process comprising the stepsof:(a) extruding a film labelstock having a heat activatable adhesivematerial, said film labelstock comprising at least a surface printablelayer; (b) printing on said surface printable layer of the filmlabelstock; (c) forming the printed film labelstock into sheets; (d)stacking the sheets; (e) die cutting the sheets on a high die cutter;(f) dispensing the die cut labels to one or more molds for applicationto an article to be labeled, wherein the film labelstock has an ultimatetensile elongation of at least about 10% in one or both of the machineand transverse directions when measured according to ASTM D-882; and (g)incorporating an edge-weld inhibiting concentration of one or more slipadditives in the film labelstock such that the stacked sheets of thelabel stock will die cut on the high die cutter without a significantdegree of edge-welding between the sheets.
 2. The invention of claim 1,wherein the sheets of film labelstock comprise at least one surfaceprintable layer defining a first outer surface of the labelstock and asupporting layer defining a second opposing outer surface of the filmlabelstock, and wherein the supporting layer is the heat activatableadhesive material as a substrate layer.
 3. The invention claim 2,wherein the edge-weld inhibiting concentration of additive is from b0.15 to 1 weight percent based on the combined weights of the surfaceprintable layer and the supporting layer.
 4. The invention of claim 2wherein the supporting layer comprises a polymeric fraction selectedfrom the group consisting of: (a) homopolymers of ethylene; (b)copolymers of ethylene with one or more alpha olefins having from 4 to 8carbons; (c) mixtures of (a) and (b); and (d) mixtures of either (a),(b), or (c) with up to 95 percent by weight of one or more copolymers ofethylene and from about 1 percent to about 30 percent by weight of acopolymerizable ethyleneically unsaturated carboxylic acid or estercontaining comonomer.
 5. The invention of claim 2 including stacking thesheets of film labelstock such that the surface printable layer of afirst sheet and the supporting layer of a second sheets are placed inintimate contact.
 6. The invention of claim 5 including incorporatingthe one or more slip additives in at least one of the surface printablelayers and the supporting layer in an amount sufficient to achieve atleast an edge-weld inhibiting concentration of said one or more slipadditives at a first outer surface of a first sheet and a secondopposing outer surface of a second sheet.
 7. The invention of claim 6,wherein the one or more slip additives are incorporated in thesupporting layer at a significantly greater concentration than in thesurface printable layer.
 8. The invention of claim 7, wherein the one ormore slip additives are incorporated substantially exclusively in thesupporting layer.
 9. The invention of claim 1 wherein the surfaceprintable layer comprises low density polyethylene or polypropylene,medium density polyethylene or polypropylene, high density polyethyleneor polypropylene, or mixtures thereof.
 10. The invention of claim 1,wherein the surface printable layer contains the heat activatableadhesive material incorporated therein.